1. Field of the Invention
The invention relates to fabricating semiconductor devices, and more particularly, to methods of fabricating highly conductive regions in semiconductor substrates for radio frequency applications.
2. Description of the Related Art
It has been a recent trend in the Si (silicon) integrated circuit industry to integrate radio transmitters and other radio frequency (RF) devices onto digital integrated circuits. Such integration requires RF shielding to prevent interference with other noise sensitive portions of the integrated circuits.
Oxidized porous Si has been used to provide effective DC (direct current) isolation. However, oxidized porous Si cannot be made too thick because of the thermal expansion coefficient mismatch between oxidized porous Si and Si. Therefore, it cannot be used for effective RF shielding, similar to silicon nitride and silicon dioxide films. On the other hand, the use of unoxidized porous Si as an insulating material has been successful in reducing RF crosstalk to a level identical to that across a vacuum.
However, there is a need in the art to further reduce crosstalk for high-end RF applications. The present invention satisfies that need.